Sealed/Inboard Bottom Brackets

Cartridge bearings are very much “fit & forget” units which work until the bearing fails, at which point they will need replacement. Some more expensive cartridge units do allow you to work on the bearings within them, but in general – units are designed to be simply thrown away and replaced over time.

The seals on these bearings keep out water and contaminants very effectively, which ultimately means more time riding and less time degreasing!

Square Taper

The square taper has been the standard type of cartridge Bottom Bracket/Crank for decades. It is still found on many off-the-peg bikes for under £500. This system stood the test of time on many types of bike up until the late 1990s, when the quest for stiffness led to the development of Bottom Bracket’s with wider diameter spindles (such as the splined systems found on the next page) and later external bearing Bottom Bracket’s.

The angled sides of the Bottom Bracket spindle and crank contact points are referred to as the taper. The crank is pulled up onto the spindle by a crank bolt which threads into the centre of the spindle.

Splined Bottom Bracket’s replaced square taper types for a few years as the standard Bottom Brackets/Crank interface. They were eventually superseded by external bearing Bottom Bracket’s, mainly due to the fact that by putting the bearing in the Bottom Bracket shell, you limit the bearing size. This relatively small shell size combined with a 20mm spindle means that the small bearings can therefore wear quickly.

WORKSHOP TIP: If replacing the more expensive Cartridge bearings, you can find the number of the bearing on the black bearing seal. A quick google search or a good bearing supplier will hopefully be able to find a replacement part for you

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